The growth in popularity of swimming pools, spas, and hot tubs has led to numerous sanitation problems caused by the difficulty of maintaining the proper chemical balance in the water. Improperly treated water leads to the proliferation of germs and bacteria. Similar sanitation problems also occur in other reservoirs of water, such as private or semi-public drinking water reservoirs, water supply tanks in recreational vehicles, cooling tower systems, etc.
Standard water sanitation methods are based on the use of chemical sanitizers, such as chlorine, bromine or ozone. In order to be effective, the sanitizers must be maintained constantly at well-defined concentration levels in the water, i.e., neither too high nor too low. This is often difficult to achieve in swimming pools and even more difficult in spas and hot tubs because of the high water temperature and the use of air jets, both of which tend to rapidly destroy or remove the sanitizer from the water. In addition, when several people get into these small bodies of water, they produce relatively large quantities of body wastes (sweat, etc.) which also deplete the sanitizer.
Pool or spa owners should, therefore, verify the chemistry of the water before anyone enters the water and even after a certain amount of time has been spent in the water. It is also necessary to add precise quantities of sanitizer as required to maintain the proper and safe concentration level thereof.
Up to now, the only practical way to verify the chemical balance in the water of most pools and spas has been with colorimetric chemical test kits using either liquid droplets, test strips or soluble tablets of a type such as that indicated generally as 10 in FIG. 1. In such a test kit, a test sample of water 12 from the pool or spa is scooped into bore 14. A staining agent 16 is then added as with the eyedropper 18. The degree of staining of the water 12 is determined, theoretically, by the amount of sanitizer in the water. This amount is then determined by comparing the degree of coloring of the water 12 against that of the preprinted test scale 20. Such test kits are inconvenient to use, complicated, and not very accurate. They can even give completely false readings in case of excess sanitizer due to bleaching of the staining solution. As a result, many people neglect the basic testing and chemical maintenance requirements and run the risk of becoming exposed to infections and diseases. These dangerous, unsanitary, and unhealthful conditions have been noted and reported by health departments all over the United States, Canada, and Europe, especially in commercial spas and hot tubs, bu also in many swimming pools.
Sophisticated electronic control systems that automatically monitor and maintain the chemistry of the water have been successfully manufactured and marketed for many years by several different companies; however, these devices are too expensive and too complicated for non-technical people and the average homeowner or small user. They also require a significant amount of maintenance, particularly for the chemical feeders. Consequently, they are used almost exclusively on large pools and spas, and not on the hundreds of thousands of smaller installations, commercial or residential, that need this type of protection just as much as the larger ones.
Recently, sanitarians at this year's National Environmental Health Association annual meeting were told that oxidation-reduction potential (ORP)--a mandatory standard for measuring water quality in West Germany's public pools and spas--ought to become a public health requirement in the United States.
Of related interest, a recently completed study of chemical and microbiological water-quality constituents for thirty public spas in the area of Portland, Oreg., found little correlation between the free-chlorine residual readings normally used to monitor them and the bacteriological quality of the spas themselves.
Normally, it is presumed that if you are maintaining a free-chlorine residual of two milligrams per liter or two parts per million (2 ppm), you have good water quality; but, the above-referenced test did not find this to be true. The only parameter that seemed to take into consideration all the constituents, including oil and grease concentration, was ORP. It was found that whenever the ORP residual was equal to or greater than 650 millivolts, the water was bacteriologically acceptable.
The National Sanitation Foundation (NSF) task committee that is currently reviewing pool and spa equipment standards, has pointed out that ORP is a well-known measurement in the field of sewage waste-water treatment. People who are knowledgeable in that area are frankly surprised that ORP is not being used for the monitoring and control of pools and spas. Public spas, in particular, are a prime target for ORP because organic loading makes potential disease transmission far more significant for public spas than for pools.
The above-referenced report suggests that bather loading, ORP, and chlorine effectiveness are directly related. The OTO chlorine test kit of FIG. 1 which is routinely sold in pool stores is unreliable because it fails to distinguish between free and combined chlorine. The parts-per-million reading determined from the stain comparison can actually be a reflection of combined chloramine, which does not protect bathers from bacteria and viruses.
Because organic and chemical loading significantly reduces the ability of free chlorine to overcome bacteria, DPD free chlorine test kits are also of questionable value unless the exact level of organic contaminant and the pH in the spa water can be determined.
West Germany's public health standards produce pool and spa water quality in that country which meets or exceeds Environmental Protection Agency drinking water standards in the United States. In West Germany, free chlorine levels of 0.2 to 0.4 ppm are considered more than adequate as long as the ORP is at an acceptable level of 650 millivolts or higher.
ORP is defined as the oxidation-reduction potential of a sanitizer such as chlorine, bromine or ozone. These oxidizers "burn off" impurities in the water, including body wastes, algae and bacteria. An ORP sensor measures the potential generated by the active form of the sanitizer, and not the inactive forms, such as combined chlorine. Unlike OTO or DPD "eyeball" testing as described above, ORP is an ongoing electronic process that requires no test chemicals or reagents and constantly monitors sanitation levels.
Persuading pool and spa industry people and public health officials to rely on ORP is a question of education and cost. NSF predicts the eventual adoption of an ORP standard for public and semi-public pool and spa facilities. Currently, a handful of manufacturers produce ORP probes, usually as a component of an automated chemical feeder system. Ironically, even managers of pools and spas who swear by chemical automation usually are unaware that ORP metering is built into these systems; the acronym is anything but a household word. ORP probes priced in the $80-100 range are now available and can monitor water on a continuous basis.
In some places, chemical automation is already mandatory. In Warren County, Ohio, for example, the General Health District requires installation of an electronic water-control device on all public spas and hot tubs to monitor and control free chlorine and pH. The same is true in Anchorage, Ak., where an automatic chlorinator with a sensor is required to insure proper levels of chlorine.
In a 1984 study in San Diego that included health club and condominium spas, out of fifty public spas surveyed, the researchers found that 24% of them were a source of parasitic infection and that more than 50% of them were under-chlorinated and had unhealthful bacteria. Thus, regardless of the costs, it is obvious that something must be done to guarantee the healthfulness of pools and spas on all levels.